Conventional archery methods of inducing arrow shaft rotation about the longitudinal spin axis primarily use variations of fletching or vanes. Launching an arrow into free flight upon release of the bowstring, air passing across fletching mounted with an angular offset to the longitudinal axis of the arrow, induces a torque about the longitudinal axis of an arrow. The net result is arrow rotation only after the arrow has traveled some distance. Features common to conventional methods require the arrow to be moving through a fluid to create the desired rotational forces. During the first moments of free flight, a current art bow launches an arrow that is not rotating about the longitudinal axis. The negative effects of zero initial rotational velocity about the longitudinal spin axis upon launch make an arrow more prone to deviate from the intended flight path. The energy required to rotationally accelerate the arrow shaft caused by prior art fletching drag robs valuable forward velocity through all phases of flight. The benefit of the physics governing conservation of angular momentum, incurred by rotation about the arrow shaft longitudinal axis, that minimize the influences of external forces, do not come into play until the arrow shaft is actually rotating. Thus, immediately upon entry into free flight, a conventional arrow loses the benefit of increased stability created by conservation of angular momentum forces until the arrow has traveled some distance.
The size of conventional fletching required to provide enough surface area necessary to get a free flight arrow rotating in a short period of time must be substantial. Once the arrow is sufficiently rotating at a latter position in the flight path, substantial fletching now causes unnecessary drag on the rotating arrow. The net result is a shorter and more parabolic flight trajectory. Additionally, fletching acts to steer an arrow into a crosswind.
In an effort to increase rotation of the arrow, known prior art devices attach vanes to the arrow shaft in a helical orientation with respect to the longitudinal axis of the arrow shaft. The helical orientation of the archery vanes generates more rotation during flight than other conventional archery vanes. However, due to the decreased clearance between archery vanes, the archery vanes interfere with an arrow rest of a bow, for example as an archer launches the arrow. This interference causes the arrow to change direction when fired from the bow or wobble during flight, resulting in decreased accuracy and flight distance. Additionally, arrow nock points require alignment or timing thus incurring an additional set-up procedure prior to launching an arrow. Further, because of a required offset position, arrows having helically oriented archery vanes are difficult to manufacture and create greater aerodynamic drag during flight.
Other conventional archery vanes have a surface with a convex shape producing an airfoil-type archery vane to generate rotation. However, the convex surface produces only a small amount of fluid displacement and relatively little rotation of the arrow during flight. Thus, these conventional archery vanes do not provide the desired rotation and stability to the arrow.
Either conventional or in the present invention, energy is required to spin an arrow. The present invention has the advantage of initially exerting energy to spin the arrow mechanically over the releasing range and thus minimizes external forces the entire period of flight, most importantly, during the first moments of free flight. The smallest deviation from intended flight path at the beginning of flight continues to grow in error as flight distance and flight time increase. A common analogy is rifling (machined spirals) located in the inner barrel bores of most guns, old and modern. Rifling acts to spin a projectile (or projectiles when referring to a shotgun) upon firing. Bullets from guns leave the barrel already spinning. No known prior art archery bows launch a pre-spinning arrow. Bullets and arrows are both projectiles with an intended flight path fighting dynamic external forces that include gravity and fluids. The disadvantage of waiting for an arrow to be moving through a fluid to create the desired rotational forces simply allows more time for introduced influential errors in the first moments of free flight.
There is an apparent need for an archery bow device that upon launch generates rotation of the arrow shaft about the longitudinal axis prior to the arrow leaving the bow thus providing increased arrow stability and flight accuracy.